Regional Heatwave Research Articles

Global emergence of regional heatwave hotspots outpaces climate model simulations

Multiple recent record-shattering weather events raise questions about the adequacy of climate models to effectively predict and prepare for unprecedented climate impacts on human life, infrastructure, and ecosystems. Here, we show that extreme heat in several regions globally is increasing significantly and faster in magnitude than what state-of-the-art climate models have predicted under present warming even after accounting for their regional summer background warming. Across all global land area, models underestimate positive trends exceeding 0.5 °C per decade in widening of the upper tail of extreme surface temperature distributions by a factor of four compared to reanalysis data and exhibit a lower fraction of significantly increasing trends overall. To a lesser degree, models also underestimate observed strong trends of contraction of the upper tails in some areas, while moderate trends are well reproduced in a global perspective. Our results highlight the need to better understand and model the drivers of extreme heat and to rapidly mitigate greenhouse gas emissions to avoid further harm from unexpected weather events.

Decadal heatwave fluctuations in China caused by the Indian and Atlantic Oceans

Heatwaves have been more common in China in recent years, largely attributed to human-caused global warming. While ocean variability, notably El Niño–Southern Oscillation (ENSO), influences regional heatwave fluctuations in China, the impact of other oceanic variability remains unclear. Here we show that the tropical Indian Ocean (TIO) and the tropical and subtropical North Atlantic Ocean (TSNAO) significantly modulate the decadal heatwave fluctuations in China. Among them, TIO has the most significant impact on northern China, while TSNAO has a greater impact on eastern China. TIO and TSNAO remotely influence heatwaves in China through abnormal sea surface temperatures (SSTs)-induced changes in atmospheric circulations involving westerlies and Rossby wave trains. Moreover, we demonstrated the physical processes responsible for heatwave fluctuations caused by TIO and TSNAO variability. The heatwave changes were determined jointly by vertical motion-related adiabatic and energy input-related diabatic temperature modifications. Our findings show that, in addition to ENSO, variability in the Indian and Atlantic Oceans is critical for understanding and predicting decadal heatwave changes in China.

Intensifying spatially compound heatwaves: Global implications to crop production and human population

Recent research has provided crucial insights on regional heatwaves, including their causal mechanisms and changes under global warming. However, detailed research on global-scale spatially compound heatwaves (SCHs) (concurrent heatwaves over multiple regions) is lacking. Here, we find statistically significant teleconnections in heatwaves and show that the frequency of global-scale SCHs and their areal extent have increased significantly, which has led to 50 % increase in the population exposed to extreme heat stresses in the two most recent decades. Crop yields were reduced in most of the years of anomalous heatwaves, which often happen during El-Niños. The internal climate variability appears to significantly influence the inter-annual variability of regional and global heatwave extents. Insights gained here are critical in better quantifying heat stress risks inflicted on socioecological systems.

Marine-cloud brightening: an airborne concept

Marine Cloud Brightening (MCB) is a proposed Solar Radiation Modification (SRM) geoengineering technique to enhance Marine Boundary Layer (MBL) cloud albedo. Extant proposals consider 104 − 105 autonomous ships spraying seawater, generating and dispersing sea salt nanoparticles. Alternatively, this paper proposes industrially manufacturing NaCl nanoparticles using ethanol anti-solvent brine precipitation. With desiccation, size optimization and narrowed size distribution, aerosol mass flux reduces by ∼500× (17× for dry mass flux). This facilitates Unmanned Aerial Vehicle delivery (e.g. MQ-9 Reaper Unmanned Aerial Vehicle). Increased speed and wake turbulence improves areal coverage per vehicle versus ships—reducing fleet size. Utilizing extant airframe designs improves vehicle Technology Readiness Level (TRL)—potentially improving system operational cost (est. $40B · yr −1) and lead time. This approach further reduces energy requirements (5× less), technical risk and system complexity. Increased readiness amplifies proliferation risk—particularly for inexpensive regional heatwave and hurricane suppression—making governance more urgent.

An Intraseasonal Dipole Mode in Summertime Surface Air Temperature over Eurasia and Its Association with Heat Wave Occurrence

Abstract A strong coherence of the summer (June–August) surface air temperature (SAT) anomalies exists over eastern Eurasia (EE) and central Eurasia (CE) in association with a remarkable intraseasonal (10–90-day) variability. The intraseasonal SAT over Eurasia shows a negative correlation between EE and CE, which is closely related to an intraseasonal wave train at the upper troposphere over the mid–high latitudes of Eurasia. The wave train propagates eastward and results in the intraseasonal variation of SAT in a seesaw pattern. The column-integrated temperature budget suggests that both the horizontal and vertical advection are important for the intraseasonal SAT dipole. More specifically, the climatological westerly, intraseasonal meridional wind anomaly, and the anomalous vertical motion play dominant roles in perturbing temperature over the CE and EE regions, while the diabatic heating is a negative feedback. The propagation of the Rossby wave train in the upper troposphere helps to maintain the circulation anomalies associated with the SAT seesaw. The leading modes of meridional wind anomalies at 200 hPa over the Eurasian high latitudes resemble the intraseasonal wave train, indicating that the wave train associated with the SAT seesaw is an atmospheric intrinsic mode over the mid–high latitudes. This study also investigates the impact of the intraseasonal SAT seesaw on regional heat wave events. It is suggested that the intraseasonal SAT seesaw has a major influence on the variability of heat wave events over both EE and CE, which may provide great implications for regional subseasonal forecasts of extreme weather events.

Suitability of the shrub-steppe habitat of Eastern Washington for Halyomorpha halys (Hemiptera: Pentatomidae).

The invasive brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera: Pentatomidae), has spread throughout most of Washington (WA) State since its detection in 2012. While it has emerged as a major agricultural and nuisance pest in the Pacific Northwest (PNW) west of the Cascade Mountains, pest pressure in the major tree fruit-growing areas in semi-arid northern and central WA State remains low. The reasons for this are unclear, although both biotic and abiotic conditions may be contributing factors. We evaluated the suitability of a common shrub-steppe/riparian corridor plant assemblage for supporting H. halys development from egg to adult in summer and fall through controlled feeding studies. Nymphs successfully completed development on this diet of PNW native plants, though it generally resulted in lower survivorship and adult weight and longer developmental times than a modified colony diet or a diet of known hosts from the eastern United States. These developmental data were used to parameterize stage-structured matrix models to predict the impact of diet and extreme heat events on H. halys population growth. The predicted net reproductive rate (R0) of H. halys was consistently and substantially reduced by a diet of PNW native plants, and heat shock imposed further severe reductions in R0. Our results suggest that the combined population effects of suboptimal plant host quality and regional heat waves may explain the lack of landscape-level H. halys pest pressure in semi-arid regions of the PNW.

Prevalent atmospheric and oceanic signals of the unprecedented heatwaves over the Yangtze River Valley in July–August 2022

Unprecedented heatwaves attacked the Yangtze River valley (YRV) in July–August of 2022. The heatwave-favorable circulation pattern for the YRV is identified by using a self-organizing map. Result shows that the dominant daily circulation pattern driving heatwaves in the YRV is the East Asian anticyclonic pattern (EAAP), characterized by an anomalous deep anticyclone over the East Asian mid-latitudes. Remarkably, the unprecedented frequent occurrence of EAAP in 2022 contributes about 84.6% of the temperature anomalies in the 35 YRV hot days, which is the key dynamical factor for the heatwave in 2022. Physical mechanisms for the occurrence of EAAP are revealed on interannual and interdecadal time scales. On interannual time scale, the dipole sea surface temperature (SST) anomalies over the North Atlantic, characterized by warm and cold SST anomalies in the midlatitudes and subtropics, respectively, exert an important influence on the EAAP days. This dipole SST pattern is unprecedentedly strong in 2022. It facilitates the EAAP through the maintenance of the coupled British–Okhotsk Corridor pattern and the Silk Road pattern in the mid-latitudes. Additionally, the persistent cold SST anomalies in tropical Indian ocean and the central-eastern Pacific from the preceding spring to summer contribute to cooling of the tropical troposphere and induce easterly anomalies in the East Asian subtropics, thereby further promoting the occurrence of EAAP. On interdecadal time scale, the negative Pacific Decadal Oscillation may establish favorable circulation conditions for the occurrence of the EAAP through modulating the interdecadal Silk Road pattern. These findings improve our understanding of the physical mechanisms for driving extreme heatwaves in the YRV and have an implication for enhancing regional heatwave prediction.

Regionalisation of heat waves in southern South America

This study describes the climatological characteristics of regional heat waves (HWs) over southern South America (SSA) for the warm seasons (October–March) of 1979–2018 based on daily maximum temperature series from 131 weather stations. Clustering of stations with high co-occurrence of simultaneous HW days is employed to identify regional HW events over five homogeneous regions: northern, central-eastern and southern SSA regions, central Argentina, and central Chile. When all regions are considered, we find a mean frequency of ∼4 HWs per year. Transitional regions (northern SSA, central-eastern SSA and central Argentina) are characterised by longer, albeit less intense, HWs than the southernmost region (southern SSA), whereas central Chile events display the lowest duration, intensity and extension. By aggregating these single HW attributes into a combined severity index, a ranking of historical HWs has been obtained, with the March 1980 event standing as the most severe one of SSA. The assessment of long-term changes reveals significant increases in the frequency of regional HW days over central Argentina and central Chile only. Trends in HW characteristics are also region dependent, and the southernmost region is the only one where HW severity has increased significantly.We report similarities and differences in the synoptic circulation patterns associated with regional HW events. Southern SSA HWs have the most distinctive signatures, related to extratropical high-pressure systems blocking the westerly flow. In the remaining regions, HWs are associated with anomalies in the South Atlantic (northern SSA, central-eastern SSA and central Argentina) or South Pacific (central Chile) High, and the intensification of the northerly low-level flow by regional thermal lows and South American Low Level Jet events. Regional HWs often migrate from northern to central-eastern SSA and central Argentina, following the displacement/intensification of the South Atlantic High, which partially explains the similarity of their associated patterns.

Immersive Cooling in the Prehospital Setting for Heat Stroke: A Case Report

Non-exertional heat stroke is defined as exposure to high outdoor temperatures, core body temperature >40 °C, and alteration of mentation. Early identification and treatment are imperative to reduce morbidity and mortality in these patients. Cold water immersion therapy is the most efficient and efficacious modality in treating heat stroke, yet it is rarely initiated in the prehospital setting. We outline a case of an 82-year-old man found unconscious outside during a regional heat wave with a temperature >107 °F. He was treated with cold water immersion using a body bag in the back of the ambulance and cooled to 104.1 °F during transport. During the 9-minute transport, the patient regained consciousness, followed basic commands, and answered basic questions. This case highlights the novel use of body bag cold water immersion as early initiation of treatment for heat stroke patients.

Regional Heatwave Prediction Using Graph Neural Network and Weather Station Data

AbstractHeatwaves lead to catastrophic consequences on public health and the economy. Accurate and timely predictions of regional heatwaves can improve climate preparedness and foster decision‐making to alleviate the burdens due to climate change. In this paper, we propose a heatwave prediction algorithm based on a novel deep learning model, that is, Graph Neural Network (GNN). This new GNN framework can provide real time warnings of the sudden occurrence of regional heatwaves with high accuracy at lower costs of computation and data collection. In addition, its interpretable structure unravels the spatiotemporal patterns of regional heatwaves and helps to enrich our understanding of the general climate dynamics and the causal influences between locations. The proposed GNN framework can be applied for the detection and prediction of other extreme or compound climate events, which calls for future studies.

Identification and Analysis of Heatwave Events Considering Temporal Continuity and Spatial Dynamics

In the context of global warming, the general increase in temperature has led to an increase in heatwave events, as well as a dramatic intensification of economic losses and social risks. This study employs the latest intensity–area–duration (IAD) framework that takes into account the temporal continuity and spatial dynamics of extreme events to identify regional heatwave events, and extracts key parameters of heatwave events to study the associated changes in frequency, intensity, influence area, and duration in seven geographic subregions of China in the 1979–2018 period. Heatwaves of all durations increased in frequency and intensity during the research period, with shorter heatwaves increasing in frequency and intensity at a faster rate than longer heatwaves. Among the seven geographic subregions, Xinjiang (XJ) and Southern China (SC) are the regions with the most frequent heatwave occurrence, while the Southwest (SW) and SC have the highest increase in heatwave frequency. In terms of regional distributions, XJ has the strongest heatwave event intensity and the largest affected area, while SC has the longest duration. However, in terms of spatial trends, SC, XJ, and the SW have the highest rates of intensity growth, influence area, and duration, respectively. In addition, heatwaves with extended durations and vast influence areas are more likely to occur in SC, and their frequency is on the rise. During the study period, the intensity, influence area, and length of heatwave occurrences in China exhibited an upward tendency, and it was shown that the longer the duration, the greater the intensity and the broader the influence area. In addition, the evolutionary characteristics of heatwave events with the longest duration indicate a certain consistency in their intensity and influence. These findings can contribute to the development of strategies to prepare for and mitigate the adverse effects of heatwave occurrences.

A Comparative Analysis of Characteristics and Synoptic Backgrounds of Extreme Heat Events over Two Urban Agglomerations in Southeast China

Based on high-resolution surface observation and reanalysis data, this paper analyzes the extreme heat events (EHEs) over two densely populated urban agglomerations in southeast China, namely the Yangtze River Delta (YRD) and the Pearl River Delta (PRD), including the spatial–temporal distribution of heatwaves and warm nights and the synoptic backgrounds for regional heatwaves. The results show that the occurrence frequency of EHEs is modulated significantly by local underlying features (i.e., land–sea contrast, terrain), and the strong nocturnal urban heat island effects make warm nights much more likely to occur in cities than rural areas during heatwaves. About 80% of the YRD regional heatwaves occur from 15 July to 15 August, while a lower fraction (53%) of the PRD heatwaves is found during this mid-summer period, which partially explains the warm-season average intensity of the former being 2–3 times the latter. A persistent, profound subtropical high is the dominant synoptic system responsible for the mid-summer YRD heatwaves, which forces significant descending motion leading to long-duration sunny weather. The mid-summer PRD heatwaves involve both high-pressure systems and tropical cyclones (TCs). A TC is present to the east of the PRD region on most (about 72%) PRD heatwave days. The organized northerly winds in the planetary boundary layer in the outer circulation of the TC transport the inland warm air, which is heated by the foehn effect at the lee side of the Nanling Mountains and possibly also the surface sensible heat flux, towards the PRD region, leading to the occurrence of the extremely high temperatures.

Extreme heatwave drives topography-dependent patterns of mortality in a bed-forming intertidal barnacle, with implications for associated community structure.

Heatwave frequency and intensity will increase as climate change progresses. Intertidal sessile invertebrates, which often form thermally benign microhabitats for associated species, are vulnerable to thermal stress because they have minimal ability to behaviourally thermoregulate. Understanding what factors influence the mortality of biogenic species and how heatwaves might impact their ability to provide habitat is critical. Here, we characterize the community associated with the thatched barnacle, Semibalanus cariosus (Pallass, 1788), in British Columbia (BC), Canada. Then, we investigate what site-level and plot-level environmental factors explained variations in barnacle mortality resulting from an unprecedented regional heatwave in BC, Canada. Furthermore, we used a manipulative shading experiment deployed prior to the heatwave to examine the effect of thermal stress on barnacle survival and recruitment and the barnacle-associated community. We identified 50 taxa inhabiting S. cariosus beds, with variations in community composition between sites. Site-scale variables and algal canopy cover did not predict S. cariosus mortality, but patch-scale variation in substratum orientation did, with more direct solar irradiance corresponding with higher barnacle mortality. The shading experiment demonstrated that S. cariosus survival, barnacle recruitment, and invertebrate community diversity were higher under shades where substratum temperatures were lower. Associated community composition also differed between shaded and non-shaded plots, suggesting S. cariosus was not able to fully buffer acute thermal stress for its associated community. While habitat provisioning by intertidal foundation species is an important source of biodiversity, these species alone may not be enough to prevent substantial community shifts following extreme heatwaves. As heatwaves become more frequent and severe, they may further reduce diversity via the loss of biogenic habitat, and spatial variation in these impacts may be substantial.

Climate warming amplified the 2020 record-breaking heatwave in the Antarctic Peninsula

February 2020 was anomalously warm in the Antarctic Peninsula region and registered one of the most intense heatwaves ever recorded in Western Antarctica. The event featured unprecedented regional mean temperature anomalies (+4.5 °C) over the Antarctic Peninsula between 6 and 11 February 2020 and the highest local temperature of the continental Antarctic region. Taking flow analogs of the event from past (1950–1984) and recent (1985–2019) periods of the ERA5 reanalysis, here we quantify the role of recent climate change in the magnitude of this 6-day regional heatwave. Results show that 2020-like heatwaves over the Antarctic Peninsula are now at least ~0.4 °C warmer than in the past period, which represents a ~25% increase in magnitude. Given the observed atmospheric circulation conditions, the probability of experiencing 6-day regional mean anomalies above ~2 °C has increased ten times since 1950–1984. The aggravated severity of the event can be largely ascribed to long-term summer warming of the Antarctic Peninsula rather than recent atmospheric circulation trends.

Early summer surface air temperature variability over Pakistan and the role of El Niño–Southern Oscillation teleconnections

AbstractEarly summer (May–June) is the season where the surface air temperature (SAT) variability is largest and may result in extreme temperature conditions over Pakistan. Therefore, we analysed the early summer interannual SAT variability over Pakistan for the period 1981–2018 using observational dataset and model simulations. We noted that upper‐level anticyclonic circulation anomalies over Pakistan, which are associated with upper to the middle tropospheric descending motion, favour clear skies with an increase in net shortwave radiation that leads to extreme surface warming over the region. Moreover, the El Niño–Southern Oscillation (ENSO) based on Niño3.4 SST index is negatively associated with SAT anomalies over Pakistan. The cold ENSO phase favours the positive geopotential height anomalies due to the strengthening of the Walker circulation that enhance the sinking motion and result in less cloudiness leading to the extreme higher surface temperature conditions over Pakistan, while the opposite happens in the warm ENSO phase. Moreover, the Saudi‐KAU Atmospheric Global Climate Model (AGCM) simulated large‐scale patterns that are in good agreement with the observations. Sensitivity experiments with the AGCM confirm that cold SST anomalies in the ENSO region significantly favour above‐normal SAT anomalies over Pakistan, while the opposite happens in the warm ENSO phase. These results are important to understand and potentially predict regional heatwaves over the South Asian region, particularly over Pakistan.

Observed sea breeze life cycle in and around NYC: Impacts on UHI and ozone patterns

This observational study investigates New York City (NYC) impacts on summer sea breeze fronts (SBFs) during a 2018 LISTOS Campaign day with a regional heat wave and O3 episode. A morning urban heat island peaked at 8.3 °C and then induced convergences into the City, trapping its NO2 emissions. SBFs came ashore at 0700 EST from the Atlantic along southern Long Island (LI), and from the LI Sound along northern LI and southern Connecticut; 2-h later another formed over New Jersey. The Ocean front was retarded over NYC at noon, while all fronts merged by 1400 EST and continued inland for four more hours. High O3 first appeared at 0900 EST downwind of NYC. By 1100 EST, a new surface peak formed north of the City in the Hudson River Valley (HRV). The maxima merged, peaking at 143 ppb at 1300 EST behind the SBF and near the maximum temperatures of 39 °C. Trajectories ending at the northern LI site with a PBL O3 peak first passed NYC, arrived before the episode, and then recirculated back in its SB flow. Trajectories ending in the HRV showed pollutant transport over NYC twice, before advection northward into the narrow Valley by the ocean SBF.

Fractional contribution of global warming and regional urbanization to intensifying regional heatwaves across Eurasia

Increasing frequency and intensity of heatwaves (HWs) in a warming climate exert catastrophic impacts on human society and natural environment. However, spatiotemporal variations of HW and their driving factors still remain obscure, especially for HW changes over Eurasia, the region with the largest population of the world. Here we provide a systematic investigation of the HW changes over Eurasia and quantify the contributions of different natural and anthropogenic factors to these changes. Increasing frequency, duration and intensity of HW are observed in most parts of Eurasia, and the occurrence of the first HW event tends to be earlier as well, especially in Europe, East Asia, Central Asia, Southwest Asia, and the Mediterranean region. These intensified HW activities are particularly stronger and more widespread after 1990 s. The spatial pattern of the increasing HW trend is closely tied to the interdecadal changes of sea surface temperature in the North Pacific. More intense hot airmass convection, atmospheric circulation obstruction over the Mediterranean region and the enhanced Mongolian high hinders the southward movement of cold air and cold and wet airmass exchange. Further analyses suggest that the intensifying Eurasian HW tendency is a combined result of both climate change and human activities. Overall, the fractional contributions of climate warming, urbanization, standardized precipitation evaporation index, and Atlantic Multi-decadal Oscillation to the frequency of Eurasian HWs are 30%, 25%, 21% and 24%, respectively. It is also suggested that the relative influential rate of different driving factors for HW varies over time and differs in different areas.

Climate change and the city: analysis of the urban heat island effect on mortality in Valencia, Spain

Abstract Background Heatwaves are increasing due to climate change and they are responsible for more fatalities than any other extreme meteorological phenomenon. An excess of mortality can occur during heatwaves, and it is usually higher in cities than in rural areas. This can be partly explained by the urban heat island effect, a human-induced modification of the local temperatures. This study assessed the effects of the July 2017 heatwave -one of the highest in recent years according to Heat Index available data- in Valencia (Spain). Methods Analytic, observational, and retrospective study on the effects of the 27-31 July 2017 heatwave in the city and province of Valencia on population mortality. Observed and expected number of deaths in our population were compared, using the same period of 2013 as a reference, and Standardized Mortality Ratio (SMR) was calculated for the capital city (urban area) and the province (suburban and rural areas) of the Valencian Region (Spain). Results The analysis showed a significant excess of mortality in the city of Valencia (787,808 pop) during the July 2017 heatwave, with an SMR of 1.634 (95% CI 1.356-1.952). In that period 116 deaths occurred, mean age 79.7 years, 50,7% women. By age groups, the population above 65 years was identified as the most vulnerable, with an SMR of 1.607 (95% CI 1.311-1.949). The mortality excess was 8% higher among men compared to women, although the difference was not significant. No significant increase in mortality was found in the province of Valencia (1,752,899 pop). Conclusions The July 2017 heatwave in the Region of Valencia brought an excess of mortality in its capital city, which did not take place in rural areas. Elderly are especially vulnerable to these extreme temperature events. Our findings raise awareness on the importance of climate change mitigation and adaptation measures, especially as regards its effects in urban areas. The regional heatwave protocol for nursing homes was enhanced. Key messages Adverse climate events are increasing due to global warming. The July 2017 heatwave in the Region of Valencia brought an excess of mortality in its capital city, especially among elderly. This study raises awareness on the need for climate change mitigation and adaptation measures, especially as regards the urban heat island effect.

Rapid rises in the magnitude and risk of extreme regional heat wave events in China

Increasing occurrence of extreme heat waves poses serious risks to human society and ecosystems. Past studies generally examined the changes in heat wave characteristics at individual stations or grid points; however, a heat wave typically appears as a regional event being continuous in time and space. Using an objective identification technique for distinguishing regional extreme events and a metric for measuring regional heat wave magnitude (i.e., an integrated index that accounts for heat wave intensity, duration, and spatial extent), this study revealed an approximate doubling in both the frequency and the magnitude of regional heat wave events observed over 1960–2018 in China. The identified top three regional heat wave events occurred in the summers of 2013, 2017, and 2003, respectively. Fine-resolution multimodel climate projections suggest that China will experience regional heat wave events with magnitude exceeding the 2013 heat event on a regular basis by 2030 under a business-as-usual scenario (RCP8.5). Compared to a 2 °C warming level, 1.5 °C warming could halve the expected occurrence of future severe regional heat wave events with magnitude similar to or slightly greater than the record-breaking one in 2013.

Heatwaves in Southeast Asia and Their Changes in a Warmer World

AbstractBased on the observational dataset SA‐OBS and model outputs from the Community Earth System Model Large Ensemble project, this study investigates heatwaves in Southeast Asia in the current and future warmer climate. A heatwave is detected when the daily maximum temperature exceeds the 90th percentile threshold at each grid for at least three consecutive days. Three characteristics describing the frequency, duration, and amplitude of heatwaves are examined, including the sum of heatwave days per year (HWF) satisfying the heatwave definition, the length of the longest yearly heatwave event (HWD), and the hottest amplitude of the hottest yearly heatwave event (HWA). Results indicate that increased global warming is associated with substantial changes in heatwave characteristics over Southeast Asia, with more frequent heatwaves, longer heatwave duration, and higher extreme temperatures. The increase in HWA has a linear growth against global warming levels with distinct regional differences between the Maritime Continent and the Indochina Peninsula due to their different heat content of lower atmospheric boundaries. In contrast, those in HWF and HWD have nonlinear growth characteristics. The projected warmer future tends to be associated with a higher risk ratio value with the occurrence of rarer extreme heatwaves relative to the current climate. These results reiterate the potential risks of extreme regional heatwaves if global warming is unrestricted.